1. Field of the Invention
The present disclosure relates to techniques of controlling a motor.
2. Description of the Related Art
As a drive source for a rotating member of an image forming apparatus, a brushless direct current (DC) motor, a brushed DC motor, a stepping motor, etc. are employed. Of these motors, the brushless DC motor typically has a Hall element, which is a sensor for detecting the position of the rotor. However, there is a sensorless brushless DC motor which does not have a Hall element as described in Japanese Patent Laid-Open No. 2003-79184.
In the sensorless brushless DC motor, the position of the rotor is detected based on an induced voltage. Therefore, when the motor is not operating, i.e., the induced voltage is absent, or when the motor is operating at low speed, i.e., the induced voltage is low, the position of the rotor cannot be detected, and therefore, an open-loop control is performed. Japanese Patent Laid-Open No. 2003-79184 describes a brushless DC motor which includes a single magnetometer and performs a drive control based on an output of the magnetometer during activation etc. However, in the configuration of Japanese Patent Laid-Open No. 2003-79184, the brushless DC motor requires the magnetometer and a magnetization pattern for the magnetometer, resulting in high cost.